This study is developing estimates for the incidence of new basal cell skin carcinoma. The importance of this study is twofold: to obtain incidence for basal cell skin carcinoma in a high risk population already exhibiting previous basal cell carcinoma lesions; and to support the basal cell skin carcinoma prevention trial launched in collaboration with the Prevention Program. (The Prevention Program is embarking on a five-year randomized double-blind clinical trial designed to evaluate the effectiveness of low dosage levels of isotretinoin in reducing the incidence of basal cell skin carcinomas in a high risk population. The estimated number of new cancer cases, excluding non-melanoma skin cancer and carcinomas in situ for 1983, is 855,000. The incidence of non-melonoma skin cancer is estimated to be approximately 400,000, of which approximately 80%, or roughly 320,000, would be basal cell carcinoma. Although basal cell carcinoma is rarely fatal, these numbers represent a big impact on the medical care system. There is some evidence that patients with a previous history of basal cell skin carcinoma as well as the broader class of non-melanoma skin cancers are more likely, depending on the number of previous tumors, to develop subsequent skin cancers. However, the studies are limited in scope. This study will explore the previous lesions and will use one of the local military centers participating in the trial.